Interpretive Summary: Rhizotonia crown and root rot of sugarbeet, caused by Rhizoctonia solani AG 2-2, is increasing in Minnesota and North Dakota. As the disease increases in prevalence and severity, more diseased roots are being stored in piles where they affect storability and postharvest quality. The objective of this research was to determine the impact of Rhizotonia crown and root rot on postharvest respiration rate, sucrose concentration, and processing quality of three sugarbeet varieties differing in resistance to Rhizotonia crown and root rot. Harvested roots, if not frozen, respire constantly to provide the energy and products needed to maintain the integrity of the root, heal wounds incurred during harvest and piling, and protect against pathogens. Respiration typically accounts for as much as 80% of the sugar lost during storage. Invert sugar is a product of sucrose breakdown that reduces processing efficiency. Respiration rates 30. 60, and 90 days after harvest (DAH) increased as disease severity increased. Respiration rates of roots with a disease rating of four (0 = no disease to 7=very severe) were slightly elevated and differences among roots with ratings of three or lower were relatively small. The respiration rate of roots with severe Rhizotonia crown and root rot (disease rating = 5) was relative high and constant during the 90 days in storage. Sucrose concentration 30 days after harvest decreased from 17.3% to 14.3% and from 17.6% to 13.8% as disease rating increased from 0 to 5 in 2010 and 2011, respectively. The increase in invert sugar concentration accompanying an increase in Rhizotonia crown and root rot severity suggests that invert sugar increased during storage and that a high frequency of roots with severe disease symptoms will reduce factory efficiency and the quality of the sugar produced.

Technical Abstract:
Rhizotonia crown and root rot of sugarbeet (Beta vulgaris L), caused by Rhizoctonia solani AG 2-2, is increasing in Minnesota and North Dakota. As the disease increases in prevalence and severity, more diseased roots are being stored in piles where they affect storability and postharvest quality. The objective of this research was to determine the impact of Rhizotonia crown and root rot on postharvest respiration rate, and processing quality of three sugarbeet varieties differing in resistance (susceptible, moderately resistant, and highest level of resistance available commercially) to Rhizotonia crown and root rot. Respiration rates 30. 60, and 90 days after harvest (DAH) increased as disease severity increased. Respiration rates of roots with a disease rating of four (0 = no disease to 7=very severe) were slightly elevated and differences among roots with ratings of three or lower were relatively small. The respiration rate of roots with severe Rhizotonia crown and root rot (disease rating = 5) was relative high and constant during the 90 days in storage. Sucrose concentration 30 days after harvest decreased from 173 g kg-1 to 143 g kg-1 and from 176 g kg-1 to 138 g kg-1 as disease rating increased from 0 to 5 in 2010 and 2011, respectively. The increase in invert sugar concentration accompanying an increase in Rhizotonia crown and root rot severity suggests that invert sugar increased during storage and that a high frequency of roots with severe disease symptoms will reduce factory efficiency and the quality of the sugar produced.